Lamp failure detection system

ABSTRACT

This application relates to a system of capacitor-discharge flash lamps which are flashed in sequence from a master timer. The invention consists of an apparatus or system for making available at the master timer information as to which lamps are flashing and which lamps are not flashing without adding wiring to the system for this purpose.

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States 111 11 1 [111 3,795,905

Wright Mar. 5, 11974 54] LAMP FAILURE DETECTION SYSTEM 3,067,411 12/1962 011111105 340/251 [75] Inventor: Donald F. wright, Dundas, Ontario, 3,715,741 2/1973 McWade et a1. 340/251 Canada Primary ExaminerDonald J. Yusko [73] Asslgnee geslqnghouse l g Assistant Examiner-Daniel Myer Omano ana a Attorney, Agent, or Firm-R, A. Stultz [22] Filed: Apr. 30, 1973 v This application relates to a system of capacitor- I llllllllllllllllllllllllll bigi fi g discharge flash lamps which are flashed in sequence [58] Mei! A 248 B from a master timer. The invention consists of an ap- 3 C paratus or system for making available at the master timer information as to which lamps are flashing and [56] References Cited which lamps are not flashing without adding wiring to UNI S S ATEN S the system for this purpose. 3,061,828 10/1962 Hauek 340/251 2 Claims, 2 Drawing Figures 1 T W 62 1 w\/ --7 PATENTEIIMR smI 33195305 ION TRANSFORMER I2 RECTIFIER I '\/V\, l r 22 24 TO TRIGGER CIRCUIT II 36 38% 4o TIMING PuLsEl l LAMP FAILURE DETECTION SYSTEM BACKGROUND OF THE INVENTION The airport approach lighting system known as a Sequenced Flash Approach Lighting System uses a number of high intensity flash lamps located on the extended center-line of a runway at distances of typically I000 feet to 3000 feet from the touchdown end of the runway, facing up the glide path. In some instances the line of lamps extends off the airport property and across adjacent fields.

The lamps are flashed in a repeated rapid sequence, the flashing of each lamp being initiated by timing pulses from a master timer located usually near the touchdown end of the runway.

Such systems, prior to the present invention, have customarily contained arrangements for monitoring the flashing of the lamps and initiating an alarm at the master timer if a prescribed number of lamps failed to flash. However these arrangements provide no information as to which lamps are not flashing. It takes a maintenance man inordinate amounts of time and travelling to locate failed lamps and to isolate troubles.

SUMMARY OF THE INVENTION In the present invention the functioning of each flash lamp is sensed by monitoring the surges of recharging current that flows into the associated energy storage capacitor (storage or energy storage means) each time it is discharged by a flash of the lamp. The presence of these current surges causes a change in the terminating impedance of the line carrying timing pulses from the master timer to the power supply of that lamp. At the master timer (timing means), the source of timing pulses for each lamp is given a sufficiently high impedance that the change in terminating impedance at the end of the timing line results in an easily detected change in the amplitude of the timing pulses going into the timing line. A test circuit (timing pulse scrutinizing or examination means) is provided at the master timer that can distinguish between the amplitude of timing pulses fed to a functioning flash lamp and the different amplitude of timing pulses fed to a non-functioning flash lamp. Thus the functional status of each flash lamp is conveyed back to the master timer via its associated timing line and no additional system wiring is needed toidentify non-functioning and functioning flash lamps.

BRIEFDESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration of the main embodiment of this invention;

FIG. 2 is a diagram of a test circuit which is capable of testing and determining which of the lamps of a particular group are inoperative.

PREFERRED EMBODIMENT OF THE INVENTION cated in the same housing with the lamp. Terminals 16 and 18 which are shown connected across energy storage capacitor 12 are connected to the power terminals of a high intensity lamp. It will also be noted that terminal 18 is grounded. A sensing circuit (timing circuit impedance altering means) 19 is connected across resistor 14. The sensing circuit consists of a capacitor 20 and a diode 22 connected directly across resistor 14. Capacitor 20 has connected in parallel therewith a Zener diode 24, a resistor 26, the base 28 of transistor 30, a collector 32 of transistor 30 and resistor 34.

The timing pulse circuit for the particular lamp which is to be connected between terminals 16 and 18 is shown originating at terminal 36. This terminal is connected into the sensing circuit 19 by means of resistor 38 which is connected to base 28 of transistor 30 as well as to emitter 40 of transistor 30. The timing pulse input terminal is also connected into the firing circuit by means of a resistor 42 which is connected to gate 44 of thyristor 46 as well as resistor 48 which is connected to ground and cathode 50 of thyristor 46. It is also to be noted that the end of resistor 48 which is connected to cathode 50 of thyristor 46 is also grounded. Before explaining in detail the operation of the circuit, a few remarks of a general nature may assist in understanding the operation. Firstly, the high intensity lamp which is to be flashed will generally be of a three terminal nature having two terminalsconnected between lines 16 and 18 and a triggering terminal which when energized will cause an arc discharge of the lamp. The triggering circuit shown in the drawing is of an illustrative nature only and many different varieties of triggering circuit are possible. However, it is believed that the sensing circuit to be described in association with resistor 14 will function with a wide variety of trigger circuits.

The circuit operates as follows. Transformer and rectifier 10 supplies energy to energy storage capacitor 12 to charge the capacitor 12 to some predetermined volt-. age. The capacitor will remain at this voltage until a triggering pulse appears on terminal 36 to initiate firing of the high intensity lamp. In this instance, the triggering pulse will flow through resistor 42 to the gate 44 of thyristor 46. Thyristor 46 becomes conductive and the triggering signal is fed to the triggering terminal of the discharge lamp which causes the discharge lamp to become conductive and subsequently discharge capacitor 12. When capacitor 12 has become sufficient ly discharged, the current flow to the lamp ceases and capacitor 12 will subsequently be recharged by. the transformerand rectifier 10. Duringthe recharge periods, resistor 14 must carry the recharging current for capacitor 12. During these periods, the side of resistor 14 connected to diode 22 assumes a negative potential as does the side of capacitor-20 connectedto diode 24. It is in this state that capacitor 20 is charged awaiting the arrival of a triggering pulse from the master timer at terminal 36. When a positive going trigger pulse is produced at terminal 36, the resultant positive signal on the lower end of resistor 38 functions in conjunction with the negative potential on the side of capacitor 20 connected to Zener diode 24 to overcome the blocking effect of the Zener diode 24, with the result that current flows and shifts the bias on the base 28 of transistor 30 to force transistor 30 to become conductive. At this time the timing pulse is able to proceed along two paths to be described. The first path is through the emitter collector circuitry of transistor 30 through resistor 34 to the grounded portion of terminal 18. The

other path is through the resistor 42 to the gate of'thy ristor 46 and through resistor 48 to ground. As long as energy storage capacitor 12 is being repeatedly recharged, capacitor remains charged and transistor conducts during each timing pulse connecting resistor 34 from the timing line to ground.

If for any reason the high intensity lamp fails to flash, capacitor 12 will not be discharged, hence no recharging operation may occur. In this instance, the voltage developed across resistor 14 will be negligible and will not be of such magnitude to charge capacitor 20. Thus even if a positive potential is produced on the lower end of resistor 38, capacitor 20 is not able to assist in turning transistor 30 on. In this instance, the triggering pulse will be faced with only the impedance of the firing circuit, that is essentially the series resistance of resistor 42 and the very low resistance from the energized gate 44 to cathode 50 of thyristor 46. The impedance change will preferably be of the order of from about 1 to 4, thus the triggering pulse may undergo a detectable increase in amplitude, e.g. from about 1 per unit to 1.7 per unit depending upon the impedance characteristics of the master timer. It will be seen now that if the triggering pulses at the master timer are examined by maintenance personnel, it will be possible to determine from the amplitude of the outgoing pulses which lamps in the group are not flashing. A circuit which will conveniently show which lamps are not flashing will be found in FIG. 2. The master timer 60 is shown having a set of terminals 62 through 70 which are connected to terminals such as 36 as shown in FIG. 1 of each discharge lamp of the installation. Terminals 62 through 70 (only a few of the terminals are shown here) will be made to be conveniently accessible at the master timer for purposes of testing and a test circuit such as the one shown in circuit 72 will be subsequently applied to each of the terminals 62 through 70 in order to determine which if any of the triggering pulses have deviated from their normal amplitude.

Test circuit 72 is shown having a probe 74, a Zener diode 76 which is paralleled by a switch 78 to which is serially connected a test lamp 80. In some instances there may be insufficient power in the timing pulses to illuminate a test lamp. It may be necessary under these circumstances to amplify the timing pulses to make observation by the human eye possible.

To test for the presence of timing pulses on any of the terminals 62 through 70, switch 78 is closed and probe 74 is connected sequentially to each of the terminals 62 through 70. A flash of the lamp under these conditions indicates that triggering pulses are present on each of the terminals. This provides an indication as to the condition of master timer 60.

To determine whether each of the lamps in the system is flashing, switch 78 is opened and again the test probe 74 is sequentially connected to terminals 62 through 70. It is by making the Zener diode 76 to have a Zener voltage which is marginally greater than the amplitude of a triggering pulse required to flash an operative lamp that this circuit is able to distinguish between the triggering pulses being applied to a flash lamp circuit which contains an inoperative lamp and one where the lamp is operative. In this instance the test lamp will flash when subjected to a triggering pulse which is of a level higher than normal. From this test, it is possible for maintenance personnel to interrogate each terminal of the master timer and immediately determine whether or not a pulse is being produced on that particular terminal and if the triggering pulse produced is in fact flashing a high intensity lamp at a location remote from the master timer.

It will be seen that this invention entails the use of no more conductors between the master timer and each high intensity lamp than would be necessary for normal operation of the circuit. This invention therefore may be conveniently applied to existing installations or applied to new installations without the addition of complex circuitry.

I claim: 1 1. Apparatus for the detection of a malfunction in the operation of a group of lamps which are arranged to flash in a periodic logical repeating sequence comprismg:

power means for supplying energy to flash each lamp of said group, 7

energy storage means associated with each lamp for storing a predetermined amount of energy for each lamp during periods when each lamp is not flashmg,

timing means for producing timing pulses which are applied to a trigger circuit associated with each lamp, to trigger each lamp into a flashing state during which time energy flows from said energy storage means into said lamp,

detecting means for continuously detecting a transfer of energy from said power means to each energy storage means,

timing circuit impedance altering means for altering the impedance of said timing circuit from a preset value during normal operation of said lamp to a significantly different value upon the detection of no energy transfer between said power means and said energy storage means over a predetermined period of time,

timing pulse scrutinizing means for examining the shape of each timing pulse produced by said timing means to determine which of any of said timing circuits have experienced a change in impedance, indicating a malfunction in the operation of a flash lamp.

2. An airport runway approach lighting system wherein a series of lamps located in predetermined spaced relationship along a runway or extension thereof are arranged to be flashed in a repeated logical sequence comprising:

power means for supplying energy to flash said lamps,

storage means associated with each lamp for storing energy delivered by said power means during periods when a respective lamp is not flashing,

timing means for producing timing pulses which are applied to a trigger circuit associated with eachlamp in a repeated logical sequence to trigger each lamp into a flashing state, said timing means producing pulses, the shape of which are dependent upon the impedance in each trigger circuit, monitoring means for continuously monitoring the flow of energy from said power means to said energy storage means, timing circuit impedance altering means for altering the impedance of said timing circuit when said monitoring means detects no appreciable energy flow between said power means and said energy storage means for a predetermined length of time, timing pulse examination means for examining each timing pulse supplied to each trigger circuit 'of said system in order to determine if the impedance of each timing circuit has been altered by said timing circuit impedance altering means. 

1. Apparatus for the detection of a malfunction in the operation of a group of lamps which are arranged to flash in a periodic logical repeating sequence comprising: power means for supplying energy to flash each lamp of said group, energy storage means aSsociated with each lamp for storing a predetermined amount of energy for each lamp during periods when each lamp is not flashing, timing means for producing timing pulses which are applied to a trigger circuit associated with each lamp, to trigger each lamp into a flashing state during which time energy flows from said energy storage means into said lamp, detecting means for continuously detecting a transfer of energy from said power means to each energy storage means, timing circuit impedance altering means for altering the impedance of said timing circuit from a preset value during normal operation of said lamp to a significantly different value upon the detection of no energy transfer between said power means and said energy storage means over a predetermined period of time, timing pulse scrutinizing means for examining the shape of each timing pulse produced by said timing means to determine which of any of said timing circuits have experienced a change in impedance, indicating a malfunction in the operation of a flash lamp.
 2. An airport runway approach lighting system wherein a series of lamps located in predetermined spaced relationship along a runway or extension thereof are arranged to be flashed in a repeated logical sequence comprising: power means for supplying energy to flash said lamps, storage means associated with each lamp for storing energy delivered by said power means during periods when a respective lamp is not flashing, timing means for producing timing pulses which are applied to a trigger circuit associated with each lamp in a repeated logical sequence to trigger each lamp into a flashing state, said timing means producing pulses, the shape of which are dependent upon the impedance in each trigger circuit, monitoring means for continuously monitoring the flow of energy from said power means to said energy storage means, timing circuit impedance altering means for altering the impedance of said timing circuit when said monitoring means detects no appreciable energy flow between said power means and said energy storage means for a predetermined length of time, timing pulse examination means for examining each timing pulse supplied to each trigger circuit of said system in order to determine if the impedance of each timing circuit has been altered by said timing circuit impedance altering means. 